Synchronizing method and apparatus



June 20, 1939. s. L. CLOTHIER ET AL SYNCHRONIZING METHOD AND APPARATUSFiled Sept. 27, 1937 1] 4, 41 A 4;" 45 i E L 45 A (A w I "page;INVENTORS Patented June 20, 1939 UNITED STATES FFECE SYN CHRONIZINGMETHOD AND APPARATUS Application September 27, 1937, Serial No. 165,794

4 Claims.

This invention relates to television and more particularly to a methodand apparatus for generating synchronizing impulses at the proper linescanning frequency.

In television systems it is essential that the scanning rate of both thetransmitter and the receiver be properly synchronized in order to obtainsatisfactory operation. By means of the present apparatus the scanningline frequency is maintained between receiver and transmitter throughthe use of synchronizing impulses which are imposed upon the electricalfluctuations emanating from the transmitting station. For example, whenthe television signals are trans mitted by radio, separate synchronizingimpulses are imposed upon the carrier preferably in intervals betweenthe successive line scans. The synchronizing impulses are employed atthe receiving station to regulate the frequency of the scanning lines,and may also be used at the transmitting station to regulate theoperation of a monitoring device.

The objects of the present invention are: to provide an improvedscanning line synchronizer which may be employed at a televisiontransmitting station to synchronize the frequency of a cathode rayscanner employed either in the transmitting or in the receivingapparatus; to provide a means for synchronizing the scanning linefrequency of a mechanical television receiver; and to provide means foradjusting the position of the scanning line synchronizer so as to obtainhorizontal framing of the picture. These and other objects of thepresent invention will become more readily apparent from the followingdescription and from the appended drawing disclosing a preferred form ofapparatus for practicing the present invention.

In the drawing:

Fig. 1 is a diagrammatic view of a mechanical transmitter adapted forscanning motion picture film showing the manner in which the scanningline synchronizer is arranged in conjunction with a scanning drum;

Fig. 2 is a detailed elevational view of the synchronizer showing themanner of mounting the synchronizing photocell;

Fig. 3 is an end view of the synchronizer shown in Fig. 2; and

Fig. 4 is a cross-sectional view of a synchronized mechanical scanner.

The invention is particularly adapted for use with a mechanicaltransmitter of the type employing a mirror drum, as herein disclosed anddescribed, in which case the mirror drum may be utilized for both thetelevision scanning and the scanning line synchronizer. A typicalarrangement embodying such an apparatus is illustrated in Fig. 1 andcomprises a scanning drum I i rotated at the desired rate by means of aconstant speed motor I2. The drum I I is provided about its peripherywith a plurality of plane reflecting surfaces I3 preferably normal tothe face of the drum Ii. When employed for scanning motion picture film,the drum is employed in conjunction with a source of high intensityillumination such as an are light I4 which is adapted to concentrate abeam of light B through a condensing lens I5 onto a transverse elongatedarea of a film F which is moved longitudinally at a constant rate ofspeed by means of sprockets It. The portion of the film illuminated bythe beam B is controlled by the shape of a slot Il formed in a mask I8positioned closely adjacent to the film F. The beam B after penetratingthe film F is focussed by means of a projection lens I9 so thatsuccessive images I of the illuminated slot I1 are formed in the planeof an aperture plate 2! after being reflected from successive surfacesI3 of the drum H. A photocell 22 is located behind the plate 2! so as toreceive imposed upon its sensitive surface the elemental areas resolvedfrom the successive images I. The responses from the photocell 22 whichcomprise the television impulses or signals are increased in amplitudeby means of a suitable signal amplifier 23 from which the signals aretransmitted as by wire or by a radio transmitter 2 to the receivingstation. The apparatus thus far described comprises a mechanicaltelevision transmitter capable of scanning motion picture film, to whichthe present invention may be applied.

The scanning line synchronizer forming a part of the present inventionmay be added directly to the film scanning mechanism and as shown inFig. 1 preferably includes .an exciter lamp 25 comprising a source ofhigh intensity illumination such as an incandescent filament, and aprojection lens capable of forming a concentrated beam of light 13 whichbeam is preferably directed so as to continually strike the same surfaceii? that the beam B impinges upon. The exciter lamp is adapted to form aconcentrated light ray or image in the plane of the synchronizeraperture plate 26.

Referring now more especially to Figs. 2 and 3, the synchronizercomprises a frame 21 secured as by means of mounting lugs 28 in fixedrelation to the drum I I. The aperture plate 26 is mounted upon theframe 2'! in any convenient manner so as to admit of adjustingsubstantially circumferentially with respect to the drum ll. This may beaccomplished as shown in Fig. 2, for example, by mounting the plate 26within longitudinal slides 29, and the sliding motion may be regulatedby means such as a threaded thumb screw 3i journalled within a bossextending from the frame 27 with the threaded stem of the screw 3iengaging a lug 32 forming a projection of the plate 26. By rotating thescrew ill the plate 26 may be moved longitudinally within the slides 29so as to alter the position of the vertical slit or aperture 33 withrespect to a fixed point on the periphery of the drum ii. A synchronizerphotocell 34 is positioned behind the plate 25 so that the beam B maystrike the sensitized photo-sensitive surface of the photocell 3A afterpassing through the slit If the desired movement of the plate 26 withinthe slides 23 is appreciable, it may be preferable to mount thephotocell in fixed relation to the plate 25 and aperture 33 as shown inFigs. 2 and 3. Accordingly the photocell socket may be mounted directlyand securely to the plate as by means of a bracket 3%. In this mannerthe photocell is moved in ac cordance with the motion of the plate 25and the position of the photocell 3 5 with respect to the slit ismaintained constant. The responses from the photocell 35 may beamplified by means of suitable synchronizer amplifier 3'! from which theimpulses may be Wired to the receiving station, or if a radiotransmitter is employed the synchronizer impulses may be superimposedupon the carrier modulated by the signals from the photocell 22. Theimpulses from the an lifier Bl may also be employed to synchronize amonitor 323 located at the transmitting station.

In operation, the aperture plate 2| is spaced from the drum ii and thelens is is adjusted so that the respective images I are separated by aslight space representing a time interval between successive lines. Thebeam B is projected upon the plate 2i with the motor l2 stationary, andthe position of the drum ii is adjusted, preferably manually, so thatthe space between adjacent images I coincides with the position of theslot in the aperture plate 2i. The excitcr lamp is then adjusted so thatthe beam B strikes the periphery of the drum M with the beam. Breflected in the general direction of the slit 33. By means of the thumbscrew 3! the plate 25 is then adjusted longitudinally until theconcentrated spot or image formed by the beam B coincides with theposition of the slit 33. Accordingly at the interval between successiveline scans the photocell 3 1 is exposed to the action of the beam B.

When the motor i2 is set in operation and the film F is moved to obtainscanning. the photocell is energized successively by the images Ireflected from the surfaces l3 about the periphery of the drum ll.During the intervals that the photocell 22 is not energized, thephotocell Sd receives impulses of constant intensity from the lamp 255at a frequency coinciding with the number of line scans formed by thedrum l l. The impulses from the photocell 34 are suitably amplified andthey may be employed to synchronize the operation of a monitor 38 byestablishing the operating frequency or they may be employed in asimilar manner to synchronize the operation of a television receiver bymeans of wire or radio transmission.

If the monitor or receiver employs a cathode ray tube, the synchronizingimpulses are utilized to synchronize the usual sweep-circuit oscillatoremployed to provide the necessary deflection voltage, in a manner wellknown in the art.

As shown in Fi 1-, the synchronizing impulses may be employed tosynchronize a mechanical receiving scanning mechanism of the typeemploying a rapidly rotating disc or drum similar to that employed atthe transmitter if the principal power employed in rotating the drum issupplied from an outside source in such a mannor that the drum rotatessubstantially at the synchronized speed.

The power is transmitted from a conventional motor through a shaft tilto a rotatable phonic wheel 4| comprising a magnetizable disc, theperiphery of which is provided with a plurality of spaced teeth 42,equal in number to the number of surfaces about the periphery of thescanning drum H, which drum is secured firmly to the shaft 39. Thesynchronizing impulses are carried through wires 43 and 44 to coils 45mounted upon a core 66, The speed control is effected by theintermittent magnetic attraction between poles 4'! and the respectiveteeth 42. If the energizing impulses for exciting the coils aretransmitted with the television signals they are filtered out andamplified in the usual manner.

Manipulation of the thumb screw 3! advances or retards the synchronizingimpulses of the photocell 34 depending upon the direction of movement ofthe plate 25. This movement is operative to properly frame the picture,in its line scan dimension.

The lamp 325 is shown projecting the beam B upon the same surface thatthe beam B is projected upon. In this manner greater precision in thesynchronizer is obtained since all error caused by angular inaccuraciesof the respective surfaces I3 is eliminated. It is to be understood,however, that if the drum is constructed with a high degree ofprecision, the beam B may be projected upon any other of the surfacesit.

Although the apparatus shown in Fig. 1 comprises a complete mechanicaltelevision transmitter the portion. of the apparatus comprising the drumH, the scanning line synchronizer S and the amplifier 3'! may beemployed in conjunction with a synchronous motor l2 as a separate andcomplete unit to provide synchronizing impulses for a cathode raytransmitting tube. Under such circumstances the operation is verysimilar to the operation of the cathode ray receiver in which theamplifier 37 is used to amplify the photocell impulses from thesynchronizer S to synchronize the sawtooth sweep oscillator whichcontrols the operation of the deflecting coils forming a part of thecathode ray transmitting tube.

It Will be readily apparent to those skilled in the art that the presentinvention may be employed in conjunction with any mechanical scanner(film, direct pickup, or flying spot) which utilizes a line scanningdrum of the type shown and described herein. Other modifications andarrangements of the hereinbefore describe apparatus may be made withoutdeparting from the spirit of the invention or sacrificing any of itsadvantages.

We claim:

1. A synchronous signal generator for use in television systemscomprising the combination with a scanning drum having a plurality ofrefleeting surfaces about its periphery, of a substantiallyconstant-intensity light source; means for directing a light beam fromsaid source upon the periphery of said drum; a synchronizing photocellin the path of the light beam reflected from said surfaces; an apertureplate positioned between said photocell and the periphery of said drum;and framing mechanism comprising means for adjusting the position ofsaid plate in a direction substantially circumferentially with respectto said drum.

2. A synchronizing signal generator for use in television systems,comprising the combination with a scanning drum having a plurality ofrefleeting surfaces about its periphery, of a substantiallyconstant-intensity light source; means for directing a light beam fromsaid source upon the periphery of said drum; a synchronizing photocellin the path of the light beam reflected from said reflecting surfaces; aframe positioned between said photocell and said drum; an aperture plateslidably mounted with respect to said frame; and means for adjustablypositioning said aperture plate with respect to said frame.

3. In a combined television scanning apparatus and synchronizing impulsegenerator having a scanning drum, phasing means comprising a frame fixedwith respect to said drum; an aperture plate slidably mounted withrespect to said frame; means for adjustably positioning said apertureplate with respect to said frame; and a photocell secured in operativerelation to said aperture plate.

4. In a television apparatus, having scanning mechanism comprising framescanning means, a rotatable line-scanning mirror drum, an apertureplate, and a photocell, said scanning means and said drum being operableto project images of successive elemental areas of the object to bescanned through said aperture plate upon said photocell to form thetelevision impulses, the combination comprising a light source, meansfor projecting light from said source upon said mirror drum, asynchronizing photocell exposed to the light successively reflected fromsaid mirror drum to thereby form synchronizing impulses, means forcombining the television impulses and said synchronizing impulses, andmeans for varying the phase relation between the synchronizing impulsesand the television impulses.

STEWART L. CLO 'II-IIER. HAROLD C. I-IOGENCAMZP.

